Fluid heaters are for example known as continuous flow heaters and are used for heating of water, which is used for sanitary purposes (e.g. shower, bath tub, sink, or hand wash basin). Typically a fluid heater has a heat source, for example a gas burner or an electric heating, and a heat exchanger. Through the heat exchanger a fluid flows, e.g. water from water supply mains or from a storage tank, wherein the water gets heated while flowing through the heat exchanger.
Depending on the water and heat demand the fluid heater or the heat source in the fluid heater is operated continuously or—at smaller heat demands—in cycle modus. The electric heating or the burner is turned on only, when a heat demand is given because of a demand by a user. The heat demand (hot water demand) is typically controlled by a flow switch.
During the operation of a fluid heater fluctuations of the outlet temperature at the tap connections may occur. During the duration of output these fluctuations result as more or less strong departures from a set temperature predetermined at the device. In this process, in particular outlet temperature peaks are unpleasant for the user, since a contact with the too hot water may lead to scalding. Also temperatures which are too low for a short time are at least inconvenient for the user.
Fluctuations of the outlet temperature may on the one hand be caused by the user of the fluid heater himself, for example by a change of the amount of water throughput during showering, or on the other hand by basic device and system conditions, which are not influenceable by the user, for example by a fluctuating gas pressure at the gas burner.
If the water is turned off during a shower for a short term or if the throughput is strongly reduced, the excess amount of heat, which is intermediately stored in the heat exchanger or the heat transmitter respectively, is introduced into the water. The amount of heat introduced by the gas burner or the electric heating into the heat exchanger is therefore also then transmitted into the water if no water throughput is happening anymore. This leads to a rapid and short term overshoot of the hot water temperature above the set temperature, and thus to undesirable temperature peaks.
If the tap is reopened after a showering stop it takes a given time offset until the gas burner transmits the needed amount of heat to the heat exchanger and thus to the water. The time offset results from the time which is necessary for firing and starting the burner as well as from the heating of its elements. Depending on the amount of throughput and the time offset this results in an undershoot of the water temperature with respect to the set temperature. The resulting surprisingly cold water is experienced by the user as inconvenient, too.
Fluid heaters are versatile used in stationary facilities (for example in bathrooms). But they can also be used in mobile areas, as for examples caravans, motorhomes or boats. The operation of fluid heater systems in mobile applications requires a special consideration of the fluctuating material and/or operation flows, since in a mobile application a central supply (for example gas supply, electric power supply, water supply) normally has to serve for several users. This may cause additional fluctuations of the hot water temperature at the tap connection, which are not expected by the user and therefore experienced as inconvenient.
From U.S. Pat. No. 8,276,548 B2 a continuous flow heater for mobile applications is known.
In DE-G-91 01 643 a water heating facility with a buffer storage is described, which is used for homogenization of the water temperature at the outlet.
Mobile applications have the additional problem that the available space is very restricted in most cases. Possible buffer or compensating reservoirs for homogenization of the temperature can therefore not readily placed in the scarce available space.
Moreover, in particular in small systems during heating the problem can appear that the water pressure rises with increasing heating such that water escapes via a pressure relief valve. Especially with the limited water reserves in mobile applications this water loss is particularly detrimental.